Internal riser rotating flow control device

ABSTRACT

A rotating flow control device, and more particularly a rotating control flow device for use inside a riser assembly during offshore drilling activities. The rotating flow control device has a stationary housing adapted to mount between the interconnected ends of riser pipe. The bearing assembly of the rotating flow control device is entirely contained within the riser pipe and maybe remotely detached and removed from the stationary housing. The rotating flow control device may be positioned in the riser such that it effectively isolates the riser slip joint from pressurized well bore returns.

FIELD OF THE INVENTION

The present invention relates to a rotating flow control device, andmore particularly to a rotating flow control device for use inside ariser.

BACKGROUND

Oil and gas offshore drilling operations require the use of a ‘riser’,or ‘riser string’ as it is also known. The riser consists of a string ofpipe that extends from a floating drilling platform down to the seafloor. The riser string is comprised of lengths of riser pipe that areattached end to end by means of flanged or custom connections. Drillingmud, cuttings and hydrocarbon products from the borehole in the seafloorare returned to the drilling platform through the riser. The top of theriser is attached to the drilling platform while its lower end issecured to the wellhead on the seafloor. Immediately below the drillingplatform, the riser has a slip joint, or tension joint as it is alsoknown, that is configured to telescope to compensate for the heave andswell that the floating drilling platform experiences in the sea. A blowout preventer (hereafter a “BOP”) is placed between the wellhead and theriser to provide protection against the sudden release of gas which canarise if the drilling operations encounter pressurized formations. Topromote safety and control, a second BOP is also frequently placed atthe top of the riser proximate to the drilling platform.

It is also conventional to use a rotating flow control device (hereaftera “RFCD”) at the level of the drilling platform in conjunction the BOP.The RFCD serves multiple purposes including the provision of a pressureseal around drill pipe that is being moved in and out of the riser andthe wellbore while allowing rotation of same. Conventional diverters arealso placed at the head of the riser above the slip joint to divertwellbore returns to the surface separation and storage equipment.

While the use of a BOP and a RFCD at the head of a riser provides apressure seal and a barrier between the external environment and thewellbore returns, such configuration can be problematic. If the lowerBOP stack fails, or if there is a sudden release of gas or pressurizedfluid into the riser for any other reason (for example; solution gasassuming gaseous form as it ascends the riser), control of thepressurized gas or fluid in the riser occurs at the level of thedrilling platform using the BOP stack, the RFCD and the diverter. Thiscan result in exposure of the drilling platform to dangerous risk if thepressure and volume of the wellbore return within the riser exceeds thepressure rating of the riser, or if the capacity of the surfaceequipment to deal with this type of event is not adequate.

The RFCD of the present invention seeks to mitigate these problems bybeing positioned in the riser string in a position below the drillingplatform and the weakest pressure rated assembly in the riser string,namely the slip joint, thus giving the riser string a greater typicalpressure integrity. The RFCD of the present invention creates a pressureseal that isolates the pressurized wellbore returns in the riser belowthe drilling platform such that it can be contained and diverted ifrequired at a subsurface level thereby substantially eliminating theexposure of the drilling platform to danger. The RFCD of the presentinvention provides an additional safety system to compliment the surfacelevel BOP and RCFD.

A subsurface RFCD is described in US 2006/0102387 to Bourgoyne et al.However, such device is integrated in the riser string such that itshousing forms part of the riser string and is therefore load bearing.Mechanical stress and pressure loads on the riser string, which has aninclination to move with the swell of the surrounding water, can impedethe mechanical performance of the RFCD and can compromise its pressureintegrity.

Accordingly, there is a need for a RFCD that can be used to create anadditional pressure seal between the wellbore and the externalenvironment which can be mounted in the riser assembly in a positionthat is below the slip joint and the drilling platform. The RFCD shouldbe configured such that it is not a load bearing component of the riserstring, thereby mitigating the risk of mechanical failure due to loadstress on the riser string. It would be preferable if the bearingassembly of the apparatus could be installed and un-installed remotelyfor maintenance, and if the device were robust and relatively simple.

SUMMARY OF THE INVENTION

In one embodiment of the present invention, the invention comprises arotating flow control device apparatus for use inside a riser, the risercomprising a string of riser pipes, each such riser pipe having two endswhereby the ends of adjacent riser pipes are interconnected to form thestring, the apparatus comprising;

-   -   (a) a tubular stationary housing mounted inside the riser, the        stationary housing having a first end and a second end, the        second end having a connector, the connector being adapted to        form part of the interconnection between the ends of two        interconnected adjacent riser pipes whereby the second end of        the stationary housing is rigidly attached to the riser and the        first end of the stationary housing is contained within but not        attached to the riser;    -   (b) a removable bearing assembly releasably mounted on the        stationary housing, the bearing assembly comprising an outer        housing, and an axially rotatable inner tubular shaft; and    -   (c) a stripper element attached to the inner tubular shaft.

In one embodiment the ends of the riser pipe are flanged and theconnector at the second end of the stationary housing is flanged. In afurther embodiment, the flanged connector of the stationary housing issandwiched between the flanged ends of the interconnected adjacent riserpipes. In a further embodiment, the flanged connector and the flangedends of the riser pipe have aligned bolt holes and bolts are employed tosecure the interconnection.

In one embodiment, the bearing assembly is releasably mounted on thestationary housing by means of a moveable latch projecting from thestationary housing that engages a complementary pocket in the outerhousing of the bearing assembly. In another embodiment, the moveablelatch is spring loaded. In further embodiments, the moveable latch maybe actuated remotely using hydraulic pressure or pneumatic pressure. Inone embodiment, there are a plurality of spring loaded latches and aplurality of complementary pockets. In another embodiment, the riserfurther comprises a slip joint and the apparatus is mounted in the riserbeneath the slip joint. In one embodiment, the stripper element iselastomeric.

In another aspect of the present invention, the invention comprises asystem for controlling pressurized wellbore returns in a riser extendingfrom a surface drilling platform to a subsea wellhead, the systemcomprising;

-   -   (a) the rotating flow control device apparatus described in the        preceding paragraphs;    -   (b) a flow spool having at least one port, the flow spool being        positioned in the riser between the apparatus and the wellhead;        and    -   (c) the at least one port of the flow spool being connected to a        pipe extending to the surface and whereby the at least one port        may be selectively opened and closed remotely from the drilling        platform.

In another aspect of the invention, the invention comprises a rotatingflow control device apparatus for use inside a conventional riser pipe,the riser pipe having a first end and a second end, the apparatuscomprising;

-   -   (a) a stationary housing having a first end and a second end;    -   (b) a bearing assembly comprising an outer housing, and an        axially rotatable inner tubular shaft, the bearing assembly        being releasably mounted on the stationary housing; and    -   (c) an elastomeric stripper element attached to the inner        tubular shaft;    -   (d) whereby the second end of the stationary housing is adapted        to rigidly attach to either the first or second end of the riser        pipe and whereby the bearing assembly is entirely contained        within the riser pipe.

In one embodiment, the ends of the riser pipe are flanged and the secondend of the stationary housing forms a complementary flanged connector.In another embodiment, the bearing assembly is releasably mounted on thestationary housing by means of a moveable latch projecting from thestationary housing that engages a complementary pocket in the outerhousing of the bearing assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like elements are assigned like reference numerals. Thedrawings are not necessarily to scale, with the emphasis instead placedupon the principles of the present invention. Additionally, each of theembodiments depicted are but one of a number of possible arrangementsutilizing the fundamental concepts of the present invention. Thedrawings are briefly described as follows:

FIG. 1 is a diagrammatic depiction of one embodiment of an offshoredrilling operation including a riser having a rotating flow controldevice of the present invention.

FIG. 2 is a diagrammatic view through a vertical cross section of oneembodiment of the apparatus of the present invention.

FIG. 3 is a diagrammatic view through a vertical cross section of ariser with one embodiment of the apparatus of the present inventionmounted therein.

FIG. 4 is a diagrammatic depiction of the flanged interconnection of twoadjacent sections of riser pipe with the flanged connection of oneembodiment of the apparatus of the present invention sandwichedtherebetween.

FIG. 5 is a diagrammatic depiction of a portion of a riser string with avertical cross sectional view of one embodiment of the apparatus of thepresent invention.

DETAILED DESCRIPTION

The invention relates to a rotating flow control device (“RFCD”) for usein the riser of an offshore drilling operation. When describing thepresent invention, all terms not defined herein have their commonart-recognized meanings. To the extent that the following description isof a specific embodiment or a particular use of the invention, it isintended to be illustrative only, and not limiting of the claimedinvention. The following description is intended to cover allalternatives, modifications and equivalents that are included in thespirit and scope of the invention, as defined in the appended claims.

Offshore oil and gas drilling operations conducted on the sea floorrequire the use of riser. As shown in FIG. 1, the riser (50) extendsfrom the drilling platform (51) down to the sea floor (53). The drillingplatform (51) may comprise a floating rig or a drill ship, or any likesurface platform employed by the offshore drilling industry.

Once a wellbore (64) has been established in the sea bed (53) and casing(62) has been cemented into place in the wellbore (64), a BOP stack (60)is landed on and secured to the well head (not shown in the figures).The BOP (60) is connected to the riser (50) which extends to thedrilling platform (51). The blow out preventer (60) is tested to ensureoperational functionality following which, drilling operations commencethrough the riser (50) in an incremental manner. Drill pipe (not shown)is lowered down through the riser (50) and drilling mud is injected downthrough the drill pipe. Drilling mud, cuttings and hydrocarbon returnsfrom the borehole travel up to the drilling platform (51) through theriser (50). Immediately below the drilling platform (51), the riser (50)has a slip joint (54) that is configured to telescope in an open andclosed fashion to compensate for the heave and swell that the floatingdrilling platform (51) experiences in the sea. The slip joint (54)prevents the riser (50) from being pulled or pushed off the well head asthe drilling platform (51) raises and lowers with the movement of thesea.

The riser (50) is comprised of a string of interconnected sections ofriser pipe (70). Commonly the riser pipe sections (70) are flanged ateach end. The flanged ends of the riser pipe sections (72) attach in acomplementary manner and are secured by bolts (74) as shown in FIGS. 4and 5. However, the description of flanged riser pipe ends is notintended to be limiting of the invention claimed herein and it will beunderstood by one skilled in the art that there are other suitable meansfor connecting the ends of riser pipes that are employed in theindustry. The apparatus of the present invention may also be used withriser pipe having such other connection means.

As shown in FIG. 1, a second BOP (65) may be employed proximate to thedrilling platform (51). As also shown in FIGS. 1 and 5, it isconventional to use a RFCD (67) at the head on the riser on the drillingplatform (51). The surface RFCD (67) serves multiple purposes includingthe provision of a pressure seal around tubular are being tripped in andout of the riser (50), and ultimately the wellbore (64) itself, whileallowing rotation of the tubulars. A conventional diverter (56) is alsoplaced at the head of the riser (50) beneath the surface RFCD (67) todivert wellbore returns from the riser (50) to the surface separationand storage equipment (not shown).

The use of a BOP (65) and a RFCD (67) at the head of a riser (50)provides a pressure seal and a barrier between the external environmentand the wellbore returns, however, such configuration can beproblematic. If the lower BOP stack (60) fails, or if there is a suddenrelease of gas or pressurized fluid into the riser for any other reason(for example; solution gas assuming gaseous form as it ascends), controlof the pressurized gas or fluid in the riser (50) occurs at the level ofthe drilling platform (51) using the BOP stack (65), the RFCD (67) andthe diverter (56). This can result in exposure of the drilling platform(51) to dangerous risk if the pressure and volume of the wellbore returnwithin the riser (50) exceeds the pressure rating of the riser (50), orif the capacity and pressure rating of the surface equipment to dealwith this type of event is not adequate. For example, should thepressure in the riser (50) exceed the weakest pressure rated link in theriser string, which is typically a 500 psi maximum pressure rated slipjoint (54) located immediately below the diverter (56) and drillingplatform (51), then to preclude mechanical failure of the riser (50) thediverter (56) is usually configured to automatically open a control portto vent the wellbore returns to relieve pressure. This results in thesudden release of pressurized hydrocarbon product at surface level thatcan potentially ignite resulting in an explosion at surface. Further, ifventing using the diverter (56) does not successfully reduce thepressure in the riser (50), mechanical failure in the riser string orthe well head may occur resulting in uncontrolled introduction ofwellbore returns into the sea and external environment.

The present invention seeks to mitigate these problems by positioning aRFCD apparatus (10) in the riser (50) in a position below both the drillplatform (51) and the weakest pressure rated assembly in the riserstring, namely the slip joint (54), thus giving the riser (50) a muchgreater typical pressure integrity. In one embodiment, a riser (50)employing the apparatus of the present invention (10) may have apressure integrity of up to 1500 psi. The RFCD of the present invention(10) creates a pressure seal that isolates the pressurized wellborereturns in the riser (50) below the drilling platform (51) such that itcan be contained and diverted if required at a subsurface level therebysubstantially eliminating the exposure of the drilling platform todanger. The RFCD of the present invention (10) provides an effectiveadditional safety system to compliment the surface level diverter (56),BOP (65) and the surface RFCD (67).

A rotating flow control device typically consists of rubber strippers orsealing elements and an associated hollow quill that rotates with thedrill string within a robust housing. Rotation of the strippers and thehollow quill is facilitated by a bearing assembly having an inner racethat rotates with the drill string and an outer race that remainsstationary with the housing. The bearing assembly is isolated from thecorrosive wellbore fluids and gases by seals.

FIG. 2 depicts one embodiment of a RFCD (10) of the present invention.As can be seen in FIG. 2, the rotating flow control device (10)comprises a stationary housing (14) having a first end (11) and a secondend (13). The second end (13) has a connector (16) adapted to rigidlyattach to the riser (50) by forming part of the interconnection betweensections of adjacent riser pipes (70). In the embodiment depicted, theconnector (16) at the second end of the stationary housing (13) isformed into a flange connection, to operatively connect with the flangedends (72) of sections of riser pipe (70). As previously described, theconnector (16) at the second end of the stationary housing (13) does nothave to be restricted to only a flanged connector with bolt holes andmay be configured to be complementary to any type of connection systemthat is being employed to connect the ends of sections of adjacent riserpipe provided that a rigid attachment to the riser (50) at the secondend of the stationary housing (13) can be achieved.

The stationary housing (14) has a bore (28) for receiving fluid and gasfrom the riser (50) and wellbore (64). The RFCD (10) has a sealedbearing assembly (15) having an axially rotatable inner tubular shaft(12) disposed therein. The inner tubular shaft (12) has an elastomericstripper element (18) supported at a downhole end of the inner tubularshaft (12). The stripper element (18) is well known in the industry andmay be constructed from any suitable rubber, elastomer or polymersubstance.

The bearing assembly (15) has a robust outer housing (22). The bearingassembly outer housing (22) and the inner tubular shaft (12) form anannular space (24) disposed in which is a bearing element (not shown).The bearing elements may comprise any suitable type used for likepurposes by those skilled in the art, and may be arranged in any mannerin the annular space (24) that provides appropriate axial and radialsupport to the inner tubular shaft (12). Any suitable lubricating fluidmay be utilized in the annular space to cool and lubricate the bearingelement. The bearing element is isolated from the wellbore fluid by alower seal (20). As shown in FIG. 2, the elastomeric stripper element(18), the lower seal (20) and the outer housing (22) of the bearingassembly (15) form a pressure seal on a tubular.

The stationary housing (14) and the outer housing of the bearingassembly (15) and the inner tubular shaft (12) may be constructed fromany suitable metallic material including, without limit, 41/30 alloysteel.

In operation, for diverting and recovering wellbore returns from theriser (50) below the RFCD (10), a flow spool (58) having one or moreports or outlets is positioned in the riser string beneath the RFCD(10). The flow spool (58) is connected to pipes or hoses (59) whichtravel to the surface for the selective discharge of well fluids andgases. The outlets in the flow spool (58) may be opened and closedremotely using surface controls to facilitate the selective venting anddiversion of the well bore returns.

As shown in FIG. 2, the stationary housing (14) defines a pocket (33)containing a spring (29) loaded metal finger or latch (30). The springs(29) are biased to urge the latch (30) in a direction towards theinterior of the housing (14). The embodiment shown depicts one continualring shaped latch, however, in an alternative embodiment there may be aplurality of discrete individual latches. The outer housing (22) of thebearing assembly (15) defines a complementary recess or pocket (31) thatreceives the latch (30) (or a plurality of pockets to receive aplurality of latches as the case may be). The latch (30) ishydraulically or pneumatically actuated remotely from the drillingplatform. Accordingly, an operator may remove and reinstall the bearingassembly (15) and associated inner tube (12) and stripper element (18)by using pneumatic or hydraulic pressure to cycle the spring loadedlatches (30). When the latch (30) is engaged in the pocket (31) of theouter housing (22) of the bearing assembly (15), the bearing assembly(15) and associated inner tube (12) will be securely held in place inthe stationary housing (14) creating a pressure seal in the riser (51).Activation of the hydraulic or pneumatic pressure will cause the latches(30) to retract by comparing the springs (29) and the bearing assembly(15), inner tube (12) and elastomeric stripper element (18) may beremoved through the riser (51). This arrangement facilitates easyremoval for maintenance and parts replacement.

It can be understood that the bearing assembly (15) and associated innertube (12) may be lowered from the drilling platform down the riserstring (50) to the stationary housing (14) when required on a tubularstring. Once in place, pressure on the latches (30) is released allowingthe springs (29) to urge the latches (30) into the pockets in the outerhousing (22) of the bearing assembly (15) to secure the bearing assembly(15) in place. The bearing assembly (15) and associated inner tube (12)may be removed following the reverse operation. If the stripper element(18) is not too compromised, removal may be effected using a tubular,however, if the stripper element (18) is unable to form an adequate sealon a tubular, then a recovery tool may be used for removal.

Although spring loaded latches and complementary pockets are detailed inthe embodiment described herein, one skilled in the art will understandthat any suitable locking system that may be remotely actuated can beemployed to releasably mount the bearing assembly (15) on the stationaryhousing (14).

If the connector (16) is configured to comprise a flange connection asshown in the Figures, it can be an API flange or can be custom sized tomatch riser pipe flange connections. As shown in FIGS. 4 and 5, in oneembodiment, the flanged connector (16) of the stationary housing (14) ofthe rotating flow control device (10) is sandwiched between the flanges(72) of two adjacent riser pipe sections (70). Bolts (74) extend throughbolt holes (75) and hold the three flanged elements together. In thismanner, the rotary flow control device (10) of the present invention maybe mounted anywhere in the riser string where there is such a flangedconnection. FIG. 1 depicts the apparatus of the present invention (10)in a riser string.

It can be understood from the Figures that once the connector (16) isrigidly attached to the riser (50) by forming part of theinterconnection between adjacent sections of riser pipe (70), thestationary housing (14) is self supporting and does not form part of theload path of the riser (50) itself. Further, the outer housing (22) ofthe bearing assembly (15) also does not form part of the load bearingriser string. Accordingly load stress placed on the riser (50) will notimpede or interfere with the performance of the RFCD (10) of the presentinvention.

Once in place, the apparatus (10) provides a seal on drill pipe orcasing that is being run into or out of the wellbore (64) and providesan additional pressure barrier between the external environment and thewellbore (64) at a subsea level below the drilling platform (51). Italso isolates the relatively weak slip joint (54) from pressurized wellbore returns.

In operation, in the event of failure of the lower BOP stack (60) or theintroduction of pressurized gas or fluid into the riser (50), the RFCD(10) of the present invention will form a pressure seal thus precludingexposure of the slip joint (54) and the drilling platform (51)components to the pressurized fluid or gas. If venting is required toreduce the pressure in the riser (50) beneath the RFCD (10), ports inthe flow spool (58) may be opened and the associated hose or pipe (59)will conduct the vented substances to a location that is a safe distancefrom the drilling platform. In this manner the RFCD (10) and the flowspool (58) comprise a system for controlling pressurized wellborereturns in a riser.

The RFCD (10) of the present invention may be employed for well controloperations, to promote safety and to mitigate environmental concerns andto manage high pressure drilling activities.

Advantages of the internal positioning of the apparatus (10) within theriser (50) include the ability to remotely install and remove thebearing assembly (15), outer housing (22), the inner tubular shaft (12)and the stripper element (18), and the protection of the apparatus (10)from the external sea water environment. Furthermore, the use of astationary housing (14) that is adapted to mount between the ends ofadjacent sections of riser pipe enables the apparatus (10) to operatewithin the riser (50) without forming an active part of the load path ofthe riser (50). It can also be understood, the apparatus of the presentinvention may be mounted within any conventional riser pipe and that itwould relatively straightforward to retrofit a riser to incorporate theapparatus of the present invention. Furthermore, the apparatus of thepresent invention is relatively simple and economical to use.

As will be apparent to those skilled in the art, various modifications,adaptations and variations of the foregoing specific disclosure can bemade without departing from the scope of the invention claimed herein.

What is claimed is:
 1. A rotating flow control device apparatus for useinside a riser, the riser comprising a string of riser pipes, each suchriser pipe having two ends whereby the ends of adjacent riser pipes areinterconnected to form the string, the apparatus comprising; (a) atubular stationary housing mounted inside the riser, the stationaryhousing having a first end and a second end, the second end having aconnector, the connector being adapted to form part of theinterconnection between the ends of two interconnected adjacent riserpipes whereby the second end of the stationary housing is rigidlyattached to the riser and the first end of the stationary housing iscontained within, but not attached to, the riser; (b) a removablebearing assembly releasably mounted on the stationary housing, thebearing assembly comprising an outer housing, and an axially rotatableinner tubular shaft; and (c) a stripper element attached to the innertubular shaft.
 2. The apparatus of claim 1 wherein the ends of the riserpipe are flanged and the connector at the second end of the stationaryhousing is flanged.
 3. The apparatus of claim 2 wherein the flangedconnector of the stationary housing is sandwiched between the flangedends of the interconnected adjacent riser pipes.
 4. The apparatus ofclaim 3 wherein the flanged connector and the flanged ends of the riserpipe have aligned bolt holes and bolts are employed to secure theinterconnection.
 5. The apparatus of claim 1 wherein the bearingassembly is releasably mounted on the stationary housing by means of amoveable latch projecting from the stationary housing that engages acomplementary pocket in the outer housing of the bearing assembly. 6.The apparatus of claim 5 wherein the moveable latch is spring loaded. 7.The apparatus of claim 5 wherein the moveable latch may be actuatedremotely using hydraulic pressure.
 8. The apparatus of claim 5 whereinthe moveable latch may be actuated remotely using pneumatic pressure. 9.The apparatus of claim 5 comprising a plurality of spring loaded latchesand a plurality of complementary pockets.
 10. The apparatus of claim 1wherein the riser further comprises a slip joint and the apparatus ismounted in the riser beneath the slip joint.
 11. The apparatus of claimI wherein the stripper element is elastomeric.
 12. A system forcontrolling pressurized wellbore returns in a riser extending from asurface drilling platform to a subsea wellhead, the system comprising;(a) the apparatus of claim 1; (b) a flow spool having at least one port,the flow spool being positioned in the riser between the apparatus andthe wellhead; and (c) the at least one port of the flow spool beingconnected to a pipe extending to the surface and whereby the at leastone port may be selectively opened and closed remotely from the drillingplatform.
 13. A rotating flow control device apparatus for use inside aconventional riser pipe, the riser pipe having a first end and a secondend, the apparatus comprising; (a) a stationary housing having a firstend and a second end; (b) a bearing assembly comprising an outerhousing, and an axially rotatable inner tubular shaft, the bearingassembly being releasably mounted on the stationary housing; (c) anelastomeric stripper element attached to the inner tubular shaft;whereby the second end of the stationary housing is adapted to rigidlyattach to either the first or second end of the riser pipe and wherebythe bearing assembly is entirely contained within the riser pipe. 14.The apparatus of claim 13 wherein the ends of the riser pipe are flangedand the second end of the stationary housing forms a complementaryflanged connector.
 15. The apparatus of claim 13 wherein the bearingassembly is releasably mounted on the stationary housing by means of amoveable latch projecting from the stationary housing that engages acomplementary pocket in the outer housing of the bearing assembly.